Why are restaurant RF gizmos so complicated?

[Joerg]

Yesterday good friends invited us to a brewpub that doesn't take
reservations but is very popular. So they have these RF doohickeys that
flash and vibrate when your table is ready. This one was clear plastic
and I scoped out what's inside. It was mind boggling:

Two chips, three (!) crystals, one resonator, one 455kHz IF filter, lots
of SMT transistors, caps, resistors and what not, plus two NiMH or
similar cells.

Why on earth are these so complicated? I mean, all they have to do is
receive a coded RF signal over a couple hundred feet of distance, then
decode it so only the one whose table is ready rings. Can't be more
daunting than a garage door opener design, can it?

Regards, Joerg

 

[[email protected]]

Two chips, three (!) crystals, one resonator, one 455kHz IF filter,
lots

of SMT transistors, caps, resistors and what not, plus two NiMH or
similar cells.

One of the chips is probably a microcontroller, one of them is the RF
receiver. One crystal for the micro's main clock, one 32.768kHz watch
crystal, one crystal for the receiver.

Or one of the chips may be an ASSP and the other may be an ISD speech
chip - many of those restaurant pagers can play music/speech to alert
you, as well as vibrating.

 

[Joerg]

Hello Lewin,

One of the chips is probably a microcontroller, one of them is the RF
receiver. One crystal for the micro's main clock, one 32.768kHz watch
crystal, one crystal for the receiver.

Yes, one must have been a uC. But nowadays they should have a DCO and
even a 32kHz crystal seems like wasted pennies here because these thing
have no need for accurate timing.

The other was a JRC chip and naturally that's where the resonator was.
But another crystal? It's all short range and when I look at our garage
door opener receivers or other RF gear in the house that stuff is
designed much lower in cost.

Or one of the chips may be an ASSP and the other may be an ISD speech
chip - many of those restaurant pagers can play music/speech to alert
you, as well as vibrating.

These just had a vibrator motor and four LEDs that flashed wildly.

Regards, Joerg

 

[Joel Kolstad]

Two chips, three (!) crystals, one resonator, one 455kHz IF filter, lots
of SMT transistors, caps, resistors and what not, plus two NiMH or similar
cells.

Why on earth are these so complicated? I mean, all they have to do is
receive a coded RF signal over a couple hundred feet of distance, then
decode it so only the one whose table is ready rings. Can't be more
daunting than a garage door opener design, can it?

If probably has a microcontroller, but other than that I'd be willing to bet
the transistor count isn't a lot different than that of a garage door
opener, even if those transistors are a little more "spread around" that in
a garage door opener (I'd bet they're using the micro to do the decoding
rather than one of the ubiquitous decoder ICs meant for garage door
openers). Some of the passive may be involved in the charging circuitry for
the batteries, which is a little bit involved if they're trying to get the
absolute longest life out of the NiMhs.

 

[martin griffith]

Why on earth are these so complicated?
Regards, Joerg

The restaurant next door /either side/in the basement with a similar
system from a competing manufacturer?

martin

"Wales is a big welsh-shaped rain collection device"

 

[Tim Hubberstey]

Two chips, three (!) crystals, one resonator, one 455kHz IF filter, lots
of SMT transistors, caps, resistors and what not, plus two NiMH or
similar cells.

Why on earth are these so complicated? I mean, all they have to do is
receive a coded RF signal over a couple hundred feet of distance, then
decode it so only the one whose table is ready rings. Can't be more
daunting than a garage door opener design, can it?

My theory on these kind of products is that the markup is so high that
the manufacturer doesn't really care how much they cost to make. My
guess is that they just threw something together quickly in order to be
early into the market.

These things are often a captive market in that they are tied to the
restaurant's billing system so competition isn't a big issue. I know of
a company where the profit on a particular product wasn't very
impressive, but the profit on the cables needed to connect it was about
$95 on a cable that sold for $100. Much like theaters - they don't make
much on the movie but they make a killing on the concessions.

 

[Guy Macon]

Yesterday good friends invited us to a brewpub that doesn't take
reservations but is very popular. So they have these RF doohickeys that
flash and vibrate when your table is ready. This one was clear plastic
and I scoped out what's inside. It was mind boggling:

Two chips, three (!) crystals, one resonator, one 455kHz IF filter, lots
of SMT transistors, caps, resistors and what not, plus two NiMH or
similar cells.

Why on earth are these so complicated? I mean, all they have to do is
receive a coded RF signal over a couple hundred feet of distance, then
decode it so only the one whose table is ready rings. Can't be more
daunting than a garage door opener design, can it?

Garage door opener; high volume, low profit margin. Reduces cost
per unit even if this makes development costs higher.

Restaurant pager; low volume, high profit margin. Reduce development
cost per unit even if this makes cost per unit higher.

 

[Joerg]

Hello Tim,

My theory on these kind of products is that the markup is so high that
the manufacturer doesn't really care how much they cost to make. My
guess is that they just threw something together quickly in order to be
early into the market.

There has to be competition. Every restaurant I went to had a different
type. Maybe not always from different mfgs though.

These things are often a captive market in that they are tied to the
restaurant's billing system so competition isn't a big issue. I know of
a company where the profit on a particular product wasn't very
impressive, but the profit on the cables needed to connect it was about
$95 on a cable that sold for $100. Much like theaters - they don't make
much on the movie but they make a killing on the concessions.

Yes, maybe. Although it wasn't NCR, the billing system. It was a
separate installation, just to organize the waiting area. Possibly
restaurant owners are too concerned about the cost of such stuff.

Theater: When I saw that they wanted more than $5 for a small bag of
popcorn we decided we didn't want popcorn. And BYOW because a small
bottle of water was in a similar price range. Go figure the markup on
that... ;-)

Regards, Joerg

 

[Joerg]

Hello Guy,

Garage door opener; high volume, low profit margin. Reduces cost
per unit even if this makes development costs higher.

They are actually quite expensive. But yes, high volume.

Restaurant pager; low volume, high profit margin. Reduce development
cost per unit even if this makes cost per unit higher.

That I don't know. The housing of these was pretty flimsy so I'd assume
that the replacement biz is humming, where R&D costs should then play a
lesser role. Then there is the old adage: If you can make it less
expensive with a reasonable effort why leave money on the table?

Regards, Joerg

 

[Joerg]

Hello Joel,

If probably has a microcontroller, but other than that I'd be willing to bet
the transistor count isn't a lot different than that of a garage door
opener, even if those transistors are a little more "spread around" that in
a garage door opener (I'd bet they're using the micro to do the decoding
rather than one of the ubiquitous decoder ICs meant for garage door
openers). Some of the passive may be involved in the charging circuitry for
the batteries, which is a little bit involved if they're trying to get the
absolute longest life out of the NiMhs.

It had a lot more parts than my garage door opener from around 1990 or
so. The reason I know is that I had to repair it recently. There were
about 30 jelly bean parts on the receiver board while this table pager
contained at least twice that many and some were higher end (the >5c
categrory), such as crystals etc.

Regards, Joerg

 

[Joerg]

Hello Martin,

The restaurant next door /either side/in the basement with a similar
system from a competing manufacturer?

Not in this case but it certainly could be elsewhere. But it's not
different with garage door openers. The new "nerd neighborhoods" around
here are so dense that you have dozens of garages per acre. Not that I
wanted to live there but from an interference point of view they don't
have any issues. Except with their WLAN stuff.

Regards, Joerg

 

[Tim Shoppa]

The housing of these was pretty flimsy

The ones I've seen are quite oversize - probably so nobody walks off
with them in their pocket without noticing. What seemed flimsy to me
about them was their unnecesarily large size and accompanying low
density.

What surprises me is that few restraunts seem to use off-the-shelf,
mass-produced pagers for this purpose. In the 80's and early 90's they
were technologically innovative in low power consumption,
miniaturization, and ruggedness. (Even better, they usually had a user
interface of at most one or two buttons). (Motorola's chips from this
era still show up in random projects because of their integration of a
complete VHF receiver and digital demodulator in a tiny
low-external-parts package.) And the vanilla pagers have got to be
cheaper. Again, maybe the problem is that vanilla pagers look like
vanilla pagers...

Tim.

 

[Joerg]

Hello Tim,

The ones I've seen are quite oversize - probably so nobody walks off
with them in their pocket without noticing. What seemed flimsy to me
about them was their unnecesarily large size and accompanying low
density.

Same with these. They were about twice the size of a pager plus a 10"
tab molded on, in a way that I can't imagine it surviving in the hands
of a rambunctuous kid.

What surprises me is that few restraunts seem to use off-the-shelf,
mass-produced pagers for this purpose. In the 80's and early 90's they
were technologically innovative in low power consumption,
miniaturization, and ruggedness. (Even better, they usually had a user
interface of at most one or two buttons). (Motorola's chips from this
era still show up in random projects because of their integration of a
complete VHF receiver and digital demodulator in a tiny
low-external-parts package.) And the vanilla pagers have got to be
cheaper. ...

That's exactly what I thought, too. Pagers and other solutions could run
off a battery voltage as low as a volt or so. If one gets stolen, so
what. It's cheap. We have made signaling receivers that cost about a
Dollar in volume plus whatever enclosure. In case of an injection mold
that would be another dime or two.

What I was hoping for was an RF extension to the MSP430 series. I didn't
go to the TI session this year but just heard from others who went that
there seems to be nothing in the pipeline. There are some RF-equipped
C51 versions from others though.

Again, maybe the problem is that vanilla pagers look like
vanilla pagers...

Well, it could always be embellished. Make it bigger. If it has to be
clear plastic add some bogus traces and sprinkle reject parts on there
to make it look fancier.

Regards, Joerg

 

[AutoTracer]

The garage door opener thing is a transmitter not a reciever. Transmitters
are generally simpler electronically. You really can't compare that to a
restruant pager. Check out the electronics on the inside of the opener and
you have a better example but even then the signaling method is likly
different as well as the frequency band making it hard to compare the
demodulation section.

These restruant recievers are just repackaged pagers and may be signalled
locally or from a cell tower like arrangement already existing to serve
pagers. Thats why they work when you wander off to the mall way across the
parking lot.

Pagers have been around for years and as such may have a whole range of
complexity from low to high integration. What you saw may not be
representative of the cutting edge which would be likly more expensive than
a well established product using parts that have been around for a while.

Even a highly integrated (1 chip) reciever/decoder would still be rather
complex inside as the reciever has to demodulate a digital signal from an
analog carrier then decode its contents to determine if the message is for
that unit or not before vibrating. Though not on these units, the chips may
also support LCD display for text messages but not inplemented.

If you think these recievers are not made cheaply enough, consider that
clear plastic cost less than colored plastic for the case (assuming non
recycled virgin material)

 

[Joerg]

Hello AutoTracer,

The garage door opener thing is a transmitter not a reciever. Transmitters
are generally simpler electronically. You really can't compare that to a
restruant pager. Check out the electronics on the inside of the opener and
you have a better example but even then the signaling method is likly
different as well as the frequency band making it hard to compare the
demodulation section.

I did compare it to door receivers, like those inside the Genie motor boxes.

These restruant recievers are just repackaged pagers and may be signalled
locally or from a cell tower like arrangement already existing to serve
pagers. Thats why they work when you wander off to the mall way across the
parking lot.

Pagers have been around for years and as such may have a whole range of
complexity from low to high integration. What you saw may not be
representative of the cutting edge which would be likly more expensive than
a well established product using parts that have been around for a while.

Maybe it wasn't cutting edge but I have seem similar ones. They contain
a lot more parts than a pager. That's what is puzzling.

Even a highly integrated (1 chip) reciever/decoder would still be rather
complex inside as the reciever has to demodulate a digital signal from an
analog carrier then decode its contents to determine if the message is for
that unit or not before vibrating. Though not on these units, the chips may
also support LCD display for text messages but not inplemented.

One-chip solutions are standard now, from several vendors. They don't
need nearly as much in discretes around them compared to what this
restaurant pager did.

If you think these recievers are not made cheaply enough, consider that
clear plastic cost less than colored plastic for the case (assuming non
recycled virgin material)

Usually black and some other dark ones are cheaper, at least when we did
them. Clear has more rejects after injection molding, you see every
speck of contaminant. Basically the plastics guys showed us a color
palette and it all cost the same. The minute we wanted something custom
it got really expensive. Then, in one case, marketing finally agreed to
a standard color: Purple! Yechhh. The downside was we had to buy several
tons of granules.

Regards, Joerg

 

[Tim Shoppa]

probably so nobody walks off

They were about twice the size of a pager plus a 10"
tab molded on, in a way that I can't imagine it surviving
in the hands of a rambunctuous kid.

Probably an explicit and important requirement is that it look nerdy
and unfashionable to the rambunctuous kids, and unnecesarily obtuse and
technologically backwards to the whiz kids .

Tim.

 

[Joerg]

Hello Tim,

Probably an explicit and important requirement is that it look nerdy
and unfashionable to the rambunctuous kids, and unnecesarily obtuse and
technologically backwards to the whiz kids .

ROFL!

On the other hand, when there is too much enticing discrete stuff on the
circuit boards under clear plastic that might tempt nerdy folks to walk
off with these things.

Regards, Joerg

 

[Paul Hovnanian P.E.]

Yesterday good friends invited us to a brewpub that doesn't take
reservations but is very popular. So they have these RF doohickeys that
flash and vibrate when your table is ready. This one was clear plastic
and I scoped out what's inside. It was mind boggling:

Two chips, three (!) crystals, one resonator, one 455kHz IF filter, lots
of SMT transistors, caps, resistors and what not, plus two NiMH or
similar cells.

Why on earth are these so complicated? I mean, all they have to do is
receive a coded RF signal over a couple hundred feet of distance, then
decode it so only the one whose table is ready rings. Can't be more
daunting than a garage door opener design, can it?

The couple of hundred feet may be misleading. Its possible that people
waiting for a table may wander quite a bit farther than that. They may
wander around shopping malls or other areas not conducive to easy r.f.
reception.

I have seen these gadgets and I believe they (some of them at least) use
a commercial pager network to broadcast signals.

 

[Keith Williams]

Hello Martin,


Not in this case but it certainly could be elsewhere. But it's not
different with garage door openers. The new "nerd neighborhoods" around
here are so dense that you have dozens of garages per acre. Not that I
wanted to live there but from an interference point of view they don't
have any issues. Except with their WLAN stuff.

They use a "garage door code" (I believe that's the term) to separate
the "keys" and add security. Basically the receiver listens to the
transmitter in a "safe mode" and remembers the key. In the normal mode,
each time that transmitter is used, the key is "incremented" (it's an
LFSR, I believe). If the receiver sees the code (give or take a
tolerance) used it updates its key and unlocks the door. If it doesn't
see its key it simply ignores it. Many openers can use the same
frequency and not interfere with each other. Likewise, it's difficult
to "pick" the lock by listening.

 

[Daniel Haude]

On Thu, 14 Apr 2005 20:31:21 GMT,

Yesterday good friends invited us to a brewpub that doesn't take
reservations but is very popular. So they have these RF doohickeys that
flash and vibrate when your table is ready.

It's amazing what people come up with. --D.